1. Field of the Invention
This invention relates generally to the field of non-destructive inspection (NDI) of structures and more particularly to a Magnetoresistive (MR) scanning array employing flexible excitation coils incorporated in a hand held positioning device.
2. Description of the Related Art
Non-destructive inspection (NDI) of a aerospace structures to detect flaws may be performed by various techniques that include X-ray radiography, ultrasonics, acoustic emissions, and eddy currents. In particular, eddy current inspection devices are commonly used for NDI of electrically conductive components. Eddy current inspection devices typically use one or more excitation coils to generate an alternating magnetic field, which in turn induces eddy currents in the component, and typically use a pickup coil to detect the magnetic field generated by the eddy currents. When an eddy current encounters an internal flaw of the component, the eddy current flows around the flaw and the resulting magnetic field generated by the eddy current is changed. The pickup coil indirectly detects this change which gives information regarding the location and size of the flaw within the component.
Magnetoresistive (MR) sensors are known for low frequency performance permitting deep feature/flaw detection in metallic structure at sensitivities considerably above those provided by convention eddy current techniques. Exemplary NDI systems employing MR are disclosed in U.S. Patent No. 6,150,809 to Tiernan et al. which uses two parallel sheets of conductors to create the magnetic field and uses a giant magnetoresistive (GMR) sensor positioned between the sheets to detect the magnetic field signals generated by eddy currents and application Ser. No. 10/923,519 entitled EDDY CURRENT INSPECTION DEVICE, having a common assignee with the present invention, the disclosure of which is incorporated herein by reference.
Current imaging scanners using MR sensors are not flexible and therefore cannot conform to the surface of the item they are inspecting. In order to be able to faithfully display the subsurface condition of a complex structure such as an aircraft, in some cases it is therefore desirable that the scanner conform to the surface shape and curvature. This allows better coupling of the inspection current into the aircraft, and prevents erroneous scan results from the “rocking” motion of a non-flexible scanner on the curved aircraft surface. Additionally, it is desirable that the scanner be mounted in a structure for operation by hand to allow a technician to accurately yet conveniently perform inspection of the desired structure.